1. Field of the Invention
The present invention relates to a lens controller. More particularly, the present invention relates to a lens controller for smoothly and accurately controlling the operation of a focusing lens group of a photographing optical system disposed on the same optical axis to a focusing position from a proximate position on this optical axis to an infinite position corresponding to the distance of a photographed object from a proximate distance to an infinite distance.
2. Description of the Related Art
With respect to a zoom lens, there is no shift in position of a formed image (a so-called focusing movement or shift) even when a zooming operation is performed. Accordingly, it is not necessary to adjust the focus every zooming operation so that the operability is improved. However, an open diaphragm F-number is in a dark state in comparison with a single focal point lens so that a skill is required to a certain extent with respect to the focusing adjustment or operation by a single-lens reflex type finder, for example.
Recently, the cameras have been automatically focused and the above problems have been solved so that the function of the zoom lens in itself can be fulfilled. Accordingly, an operator or user can pay attention to only the determination of a composition along the photographing intention, thereby greatly improving the operability.
In general, a focusing operation of a zoom lens is performed by moving a focusing lens group disposed in a portion of a zoom optical system. The zoom lens has the advantages that the moving amount of this focusing lens group is approximately the same with respect to the same distance of a photographed object in an entire zoom region (which is called "equal amount movement" in the following description). Accordingly, it is enough to attach a scale for the distance of the photographed object to a moving member (distance ring) of the focusing lens group, and attach an index to a fixed ring adjacent to this moving member. Therefore, it is not necessary to change the scale for the distance of the photographed object in response to the zooming operation.
However, in the zoom lenses in an inner focusing system and a rear focusing system, the lens construction is complicated when an optical design is performed under a condition in which the above-mentioned equal amount movement is realized. Further, the moving amount (drawing-out amount) of the focusing lens group on a wide angle side is excessively large. Such problems are different in extent from each other depending on the lens construction of the above-mentioned zoom optical systems. Further, by these problems, the outer diameter of a lens becomes large so that the lens and its body tube become heavy.
As mentioned above, a operability of the zoom lens is improved by the combination of the zoom lens and the automatically focusing function. However, the condition of the above equal amount movement with respect to the zoom lens must be satisfied. Therefore, it is still difficult to make the lens controller compact and reduce the cost thereof.
Therefore, the applicant of this application has proposed a varifocal lens controller for solving the above-mentioned problems as an invention (which is called the invention of the prior application in the following description) in Japanese Patent Application No. 62-013345 (see Japanese Patent Application Laying Open (KOKAI) No. 63-182620).
Namely, the above invention of the prior application relates to a lens controller for controlling the operation of a varifocal lens. In this invention, a zoom optical system is composed of a zoom lens group and a focusing lens group disposed on the same optical axis. The focusing lens group is set in a focusing position from a proximate position to an infinite position on the optical axis corresponding to the distance of a photographed object from a proximate distance to an infinite distance. Thereafter, the controller controls the operation of the varifocal lens causing a shift in position of a formed image with respect to the same photographed object by changing the zoom lens group a focal distance of the entire zoom optical system from an arbitrary first focal distance to a second focal distance between a shortest focal distance and a longest focal distance.
This lens controller comprises focal distance detecting means for detecting the above focal distance of the entire lens system; focusing lens group position detecting means for detecting the position of the above focusing lens group on the above optical axis; and maximum drawing-out amount calculating means for receiving an output of the above focal distance detecting means and calculating a drawing-out amount of the above focusing lens group from the above infinite position to the above proximate position with respect to the above focal distance. The lens controller further comprises proportional constant calculating means for respectively receiving outputs of the maximum drawing-out amount calculating means and the above focusing lens group position detecting means and calculating a ratio of these outputs. The lens controller further comprises focusing correction calculating means for respective outputs of the proportional constant calculating means, the above maximum drawing-out amount calculating means and the above focusing lens group position detecting means and calculating, as a correction value, a shift amount of the position of the formed image from the above focusing position caused by the change in focal distance of the entire lens system. The lens controller further comprises focusing drive means for driving the above focusing lens group; and moving amount monitoring means for generating a signal corresponding to the moving amount of the above focusing lens group. The lens controller further comprises focusing control means for respectively receiving outputs of this moving amount monitoring means and the above focusing correction calculating means and controlling the above focusing lens group to move to the above focusing position. The lens controller further comprises zoom drive means for driving the above zoom lens group; and zoom control means for receiving a start signal from start means separately disposed and controlling the operation of the above zoom drive means. The lens controller is constructed to automatically correct the shift in position of the formed image caused by the change in focal distance of the above entire zoom optical system.
In the automatically focusing camera, to obtain information of the photographing distance, the position (the drawing-out amount) of the focusing lens after the focusing operation is detected and the information of the photographing distance is calculated on the basis of the detected position information.
The applicant of this application has proposed an invention with respect to a display of the photographing distance in Japanese Patent Application Laying Open (KOKAI) No. 63-291018, for example, and an invention with respect to a shift correction in Japanese Patent Application Laying Open (KOKAI) No. 63-182620, for example.
In accordance with the structure of the above invention in Japanese Patent Application Laying Open (KOKAI) No. 63-182620, the lens optical system has a very simple construction and is compact, light and cheaply manufactured. Further, the entire lens controller is similarly compact, light and cheaply manufactured. Further, in this lens controller, even when the zoom lens group is moved from an arbitrary first focal distance to a second focal distance to change the focal distance of the entire lens system, the shift in position of a formed image peculiar to a varifocal lens can be instantly corrected and a focusing state can be held. Accordingly, a lens similar to the zoom lens can be substantially obtained in use.
However, in a certain case, the above varifocal lens is constructed such that the focusing position in the infinite position (.infin. position) is not changed and the focusing position in the proximate position is changed to move away from the infinite position with respect to the change in focal distance of the entire lens system from the above shortest focal distance to the longest focal distance. For example, when the operation of the focusing lens group is controlled while the zooming operation of the zoom lens group is performed from the long focal point side to the short focal point side, conversely, from the short focal point side to the long focal point side, it is proved that this focusing lens group hits against a positioning member such as a stopper, etc. in the infinite and proximate positions and thereby cannot be moved so that the controller is disabled and an excessive load is applied to a drive motor.
Further, similar to the above case, there is a problem about the hit against the positioning member even when the photographing lens is constructed by a zoom lens instead of the varifocal lens, and even when the focusing lens group is driven to perform the focusing adjustment without changing the focal distance.
Further, when the focusing lens group is driven on the basis of information about the measured distance from a distance measuring means, the focusing lens group is not driven or stopped with only one point as a target, but a predetermined width (generally, the width in a very small range approximately corresponding to the depth of the photographed object) is set. When the focusing lens group is driven within this width (focusing width), the lens group is set to be operated in a focusing state. This construction is provided to prevent mechanical errors, the hunting of the control system, etc. Accordingly, there is a problem about the reduction of the accuracy in information of the photographing distance provided from the position information of the focusing lens group.
When the zoom lens, etc. are used, the above focusing width is wider in a wide position than in a telescopic position and the accuracy in information of the above photographing distance is further reduced even when the F number is same.
Further, similar problems are caused even when the varifocal lens is used.